Q I've been told that my tomatoes have blossom end rot. What is this?

A This is a physiological problem and causes dark, leathery patches at the blossom end of the fruits. It’s not a disease.

Caption: Affected fruit are best removed as they won't develop further

Q What causes blossom end rot?

A The immediate cause is a shortage of calcium in the developing fruit. The usual reason for this is erratic and/or inadequate watering, plus high temperatures.

Q Can I just add extra calcium to the soil to treat blossom end rot?

A Unfortunately, this problem does not usually mean that the soil or compost is deficient in calcium, rather that the plant does not have a sufficiently steady water supply to deliver it to the fruit. This problem is most common with tomatoes grown in growing bags, as it is difficult to keep these well watered.

Q Can I still eat tomatoes affected by blossom end rot?

A Yes. If the tomato is ripe, cut out the dark patch and eat the rest. If it's not ripe, the damage is likely to prevent further development, and affected fruit are best removed.

Q Can blossom end rot be cured?

A You can't cure a damaged tomato, but you can help to prevent the problem getting worse or damaging other fruit.

Try to reduce the temperature of the greenhouse or growing area by shading and/or ventilation and water more frequently.

If you are using growing bags lying on soil, keep the soil well-watered and cut slits in the base of the growing bags so the roots can explore further for water – this will not lead to disease problems in the soil.

To prevent the problem in future, avoid growing bags if possible. Either grow tomatoes by ring culture; or in large (30cm) tubs; or in growing bags cut in half and stood on end to make two deep bags of compost.

Ring culture involves growing your tomato plants in large (22-26cm), bottomless pots. These should be filled with compost and stood on a water-retaining, though free-draining, base, such as a shallow trench lined with polythene and filled in with gravel.

Water from the bottom via the gravel bed and feed via the pot. This way the tomatoes have a free-draining system with water and feed available as and when they need it.

Caption: Open the greenhouse doors and windows to reduce the temperature